X-ray flare from a dim source

Last Dec. 15, the Chandra X-ray Observatory stared at an old, failed star for 9 hours and saw absolutely nothing. That’s just what Gibor Basri of the University of California, Berkeley was hoping. The absence of radiation confirms that as failed stars, known as brown dwarfs, grow older, they lose their hot outer atmosphere, or corona, and can’t readily generate X-ray flares, he says.

But there appears to be some life left in these fading objects, which lack the mass to burn steadily as bona fide stars. Nine hours into the 12-hour observation of the aging brown dwarf LP 944-20, an X-ray flare smacked the telescope.

Jolted by the result, Basri says the lone flare indicates that although older brown dwarfs don’t have a corona, they do have magnetic fields that can occasionally generate storms beneath the surface of the failed star. These flares sometimes punch through into the cool atmosphere of the dwarf.

Basri and his colleagues are scheduled to report their findings in an upcoming Astrophysical Journal Letters.

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